I. Field of the Invention
The present invention relates to a process for manufacturing a plastic hollow body, and in particular, a fuel tank, and this from a parison that is split or is in two parts. It also relates to a die for extruding a parison suitable for said process.
II. Description of Related Art
Fuel systems on board vehicles of various types generally comprise devices for the ventilation of hydrocarbons contained in the tank. They may also include devices for supplying the engine with fuel. Such devices form the link between elements contained in the tank (valves, fuel pump, etc.) and elements positioned outside the tank (canister, filling pipe, etc.). The penetration through the wall of the tank must take into account the sealing requirements laid down by current environmental standards (LEV II and PZEV for example). For this purpose, the reduction in the number and size of the openings in the wall of the tank constitutes a favourable factor in reducing evaporative losses. However, this makes it more difficult to insert components into the tank and position them therein.
Application EP 1110697 in the name of the Applicant discloses a process for moulding a fuel tank using a parison in several parts so as to be able to insert the accessories into the tank at the same time as it is moulded. For this purpose, a tubular parison is extruded, then, on exiting the die, two longitudinal cuts are made in it, along two opposing generatrices. This document recommends the use of a device for guiding and separating the two parison parts thus obtained, and this with a view to being able to introduce the accessories into the tank at the same time as it is moulded.
Ideally, this device should also make it possible to substantially flatten the two parison parts and keep them free of bends so as to be able to apply them correctly between the mould cavities. This may be carried out using straight cylindrical rollers or rolls, the separation of which is set at will. This simple (and theoretically adequate) technique has, however, the disadvantage that the sheets obtained on exiting the rolls remain, after all, curved and that their separation cannot be well controlled. This is because the plastic begins to set as soon as it exits the die and tends to remain in the shape that the die gives it.